Calibration of imaging plate for high energy electron spectrometer

Copyright 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Review of Scientific Instruments, 76(1), 013507_1-013507_5, 2005 and may be found at http://dx.doi.org/10.1063/1.182437

Cryogenic deuterium target experiments with the GEKKO XII, green laser system

Copyright 1995 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Physics of Plasmas, 2(6), 2495-2503, 1995 and may be found at http://dx.doi.org/10.1063/1.87121

Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments

In high-energy-density physics, including inertial fusion energy using high-power lasers, doping tracer atoms and deuteration of target materials play an important role in diagnosis. For example, a low-concentration Cu dopant acts as an x-ray source for electron temperature detection while a deuterium dopant acts as a neutron source for fusion reaction detection. However, the simultaneous achievement of Cu doping, a deuterated polymer, mechanical toughness and chemical robustness during the fabrication process is not so simple. In this study, we report the successful fabrication of a Cu-doped deuterated target. The obtained samples were characterized by inductively coupled plasma optical emission spectrometry, differential scanning calorimetry and Fourier transform infrared spectroscopy. Simultaneous measurements of Cu K-shell x-ray emission and beam fusion neutrons were demonstrated using a petawatt laser at Osaka University.Ikeda T., Kaneyasu Y., Hosokawa H., et al. Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments. Nuclear Fusion 63, 016010 (2023); https://doi.org/10.1088/1741-4326/aca2ba

Hot electron and ion spectra on blow-off plasma free target in GXII-LFEX direct fast ignition experiment

Polystyrene deuteride shell targets with two holes were imploded by the Gekko XII laser and additionally heated by the LFEX laser in a direct fast ignition experiment. In general, when an ultra-intense laser is injected into a blow-off plasma created by the imploding laser, electrons are generated far from the target core and the energies of electrons increase because the electron acceleration distance has been extended. The blow-off plasma moves not only to the vertical direction but to the lateral direction against the target surface. In a shell target with holes, a lower effective electron temperature can be realized by reducing the inflow of the implosion plasma onto the LFEX path, and high coupling efficiency can be expected. The energies of hot electrons and ions absorbed into the target core were calculated from the energy spectra using three electron energy spectrometers and a neutron time-of-flight measurement system, Mandala. The ions have a large contribution of 74% (electron heating of 4.9 J and ion heating of 14.1 J) to target heating in direct fast ignition

Demonstration of a spherical plasma mirror for the counter-propagating kilojoule-class petawatt LFEX laser system

A counter-propagating laser-beam platform using a spherical plasma mirror was developed for the kilojoule-class petawatt LFEX laser. The temporal and spatial overlaps of the incoming and redirected beams were measured with an optical interferometer and an x-ray pinhole camera. The plasma mirror performance was evaluated by measuring fast electrons, ions, and neutrons generated in the counter-propagating laser interaction with a Cu-doped deuterated film on both sides. The reflectivity and peak intensity were estimated as ∼50% and ∼5 × 1018 W/cm2, respectively. The platform could enable studies of counter-streaming charged particles in high-energy-density plasmas for fundamental and inertial confinement fusion research.Kojima S., Abe Y., Miura E., et al. Demonstration of a spherical plasma mirror for the counter-propagating kilojoule-class petawatt LFEX laser system. Optics Express 30, 43491 (2022); https://doi.org/10.1364/oe.475945

Direct fast heating efficiency of a counter-imploded core plasma employing a laser for fast ignition experiments (LFEX)

Fast heating efficiency when a pre-imploded core is directly heated with an ultraintense laser (heating laser) was investigated. \u27Direct heating\u27 means that a heating laser hits a pre-imploded core without applying either a laser guiding cone or an external field. The efficiency, η, is defined as the increase in the internal core energy divided by the energy of the heating laser. Six beams (output of 1.6 kJ) from the GEKKO XII (GXII) green laser system at the Institute of Laser Engineering (ILE), Osaka University were applied to implode a spherical deuterated polystyrene (CD) shell target to form a dense core. The DD-reacted protons and the core x-ray emissions showed a core density of 2.8 ± 0.7 g cm−3, or 2.6 times the solid density. Furthermore, DD-reacted thermal neutrons were utilized to estimate the core temperature between 600 and 750 eV. Thereafter, the core was directly heated by a laser for fast-ignition experiments (LFEX, an extremely energetic ultrashort pulse laser) at ILE with its axis lying along or perpendicular to the GXII bundle axis, respectively. The former and latter laser configurations were termed \u27axial\u27 and \u27transverse modes\u27, respectively. The η was estimated from three independent methods: (1) the core x-ray emission, (2) the thermal neutron yield, and (3) the runaway hot electron spectra. For the axial mode, 0.8%< η <2.1% at low power (low LFEX energy) and 0.4%< η <2.5% at high power (high LFEX energy). For the transverse mode, 2.6%< η <7% at low power and 1.5%< η <7.7% at high power. Their efficiencies were compared with that in the uniform implosion mode using 12 GXII beams, 6% < η <12%, which appeared near to the η for the transverse mode, except that the error bar is very large

Fabrication of high-concentration Cu-doped deuterated targets for fast ignition experiments

先端科学・社会共創推進機構In high-energy-density physics, including inertial fusion energy using high-power lasers, doping tracer atoms and deuteration of target materials play an important role in diagnosis. For example, a low-concentration Cu dopant acts as an x-ray source for electron temperature detection while a deuterium dopant acts as a neutron source for fusion reaction detection. However, the simultaneous achievement of Cu doping, a deuterated polymer, mechanical toughness and chemical robustness during the fabrication process is not so simple. In this study, we report the successful fabrication of a Cu-doped deuterated target. The obtained samples were characterized by inductively coupled plasma optical emission spectrometry, differential scanning calorimetry and Fourier transform infrared spectroscopy. Simultaneous measurements of Cu K-shell x-ray emission and beam fusion neutrons were demonstrated using a petawatt laser at Osaka University

Electron Acceleration in an Ultra-intense Laser Illuminated Capillary and Its Application

A gas jet is mainly used for the plasma source, limiting the acceleration length to 2 mm or less. This is only a few times larger than the Rayleigh range, in which the laser spot size increases by $\sqrt{2}$ and is written as ${z_R} = \pi r_0^2/\lambda_0$, where $r_0$ is a laser spot radius and $\lambda_0$ is the laser wavelength. Even though the ultra-intense lasers have dramatically increased the acceleration gradient from one GV/m of the above-mentioned CO$_2$ laser beatwave to hundreds GV/m of a self-modulated wakefield or other scheme, nevertheless, nothing makes the plasma length longer. The acceleration gain is, therefore, limited to a few hundreds MeV level. Suppose an plasma, whose size is much longer than ${z_R}$ and close to the dephasing limit, given by $\lambda_p\gamma_\phi^2/\pi$, where $\lambda_p$ is the plasma wave length and square of a relativistic factor $\gamma_\phi^2$ is a ratio of the cutoff plasma density $n_c$ to the electron density $n_e$. The dephasing limit is typically 30 cm for $10^{17}$cm$^{-3}$. In the relativistic laser regime, the maximum acceleration field is approximated by $E_{max} \sim E_{wb}a_0 = m\omega_pca_0/e \sim E_L/{\gamma_\phi},$ where $E_{wb}$ is the classical wavebreaking field $\sim30\sqrt{n_e/10^{17}\rm{cm}^{-3}}$ [GV/m], and $a_0$ the normalized laser field $eE_L/{m\omega_0c}$. If, then, a laser of $a_0 = 2$ transmits 30 cm under a $10^{17}$cm$^{-3}$ plasma, electrons obtain the gain $eE_{max} \times 30$ cm $>18$ GeV. Many theoretical and experimental efforts, such as z-pinch, axicon channel and capillaries, are dedicated to make the acceleration length longer. On the other hand, the maximum energy gain $W_{max}$, which the electron can obtain within the dephasing limit, can be written as $2mc^2\gamma_\phi^2a_0^2/\sqrt{1+a_0^2/2}$. So if you want to have GeV electrons, since $a_0$ is $1 \sim 4$ for $2 \times 10^{18} \sim 2\times 10^{19}$ Wcm$^{-2}$, $\gamma_\phi$ must be larger than 15, which means that the electron density must be less than $10^{19}$ cm$^{-3}$. Then, we need a thin but cm -class plasma. Some have realized $2 \sim10$ cm plasma columns, but no electron acceleration has been yet reported. Here the 1-cm long or longer capillary accelerations of electrons are presented\cite{YK}. A 1-mm long cone, attached to the entrance edge, guides the laser beam into the capillary. The laser ablates plasmas in the order of $10^{16}$ cm$^{-3}$ from the capillary wall. We show a energy bump due to the trapping. Both the GMII laser of 15 J -1.053 $\mu$m pulse in $0.5$ ps and the PW laser of 150 J -1.053 $\mu$m pulse in $0.6$ ps were injected into the glass capillaries of 1 to 7 cm in length and 30 to 150 $\mu$m in bore size, which accelerated plasma electrons to 100 MeV via the laser wakefield inside the capillary. The plasma length was longer than any gas jet plasmas. The one and two-dimensional Particle-In-Cell simulations show the middle energy shoulder. The simulations describe that the capillary sustains a 10 GV/m laser wakefield. The particle trapping and the resulting bunch are explained by the simulation, which is the important steps to cool the accelerated beams. The PIC simulations well described the capillary acceleration, since the capillary confines the laser pulse as well as the plasma over a distance much longer than $z_R$. The application of the capillary accelerator will be discussed. {YK} Y. Kitagawa {\it et al.}, Phys. Rev. Lett. {\bf 92}, 205002(2004).レーザーとビーム相互作用及びレーザーとプラズマの加速器に関するICFAワークショッ